Electric Power Steering Overheat Protection Logic
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Solution Overview
Problem
Existing electric power steering systems face issues with overheat protection units that may fail due to errors in computing heat dissipation states, leading to potential damage to the ECU and motor, and these systems become expensive when independent arithmetic units are used for monitoring.
Innovation Solution
An electric power steering system that computes an overheat protection current value based on steering wheel torque and stores this value for comparison with newly computed values, using a control unit to limit motor current and prevent overheating, thus providing a reliable and cost-effective solution.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If an independent arithmetic unit is used to monitor computation errors in the overheat protection unit, then the reliability of the system is improved, but the system cost increases
Solution Approach 1:
The monitoring function is merged with the existing overheat protection control unit rather than using a separate independent arithmetic unit. The control unit performs both the overheat protection computation and the error monitoring functions, reducing system cost while maintaining reliability through internal self-checking mechanisms.
Solution Approach 2:
The overheat protection control unit performs self-monitoring of its own computation processes. By using the same control unit to both execute the overheat protection algorithm and monitor for computation errors, the system achieves self-service capability without requiring additional external monitoring hardware.
2Reliability
If the overheat protection unit uses cumulative current values to determine heat dissipation states, then the protection function is provided, but computation errors may occur leading to insufficient or excessive current limitation
Solution Approach 1:
The system implements feedback by comparing the newly computed overheat protection current value with the previously stored value. This feedback mechanism detects computation errors by identifying abnormal changes between consecutive computations, ensuring accurate current limitation decisions and preventing both insufficient and excessive protection.
Solution Approach 2:
The system stores the previously computed overheat protection current value before performing the new computation. This preliminary storage of reference data enables subsequent comparison to detect computation errors, allowing the system to identify and correct abnormal values before they affect motor current control.
Data Source
AI summary
An electric power steering system includes an overheat protection current value arithmetic unit that computes an overheat protection current value to which a current flowing into a motor is limited, and an overheat protection control unit that limits the current, which flows into the motor, on the basis of the computed overheat protection current value, suppresses heat dissipation caused by the current flowing into the motor, and thus protects onboard equipment. Information relevant to the computed overheat protection current value is stored. Whether a newly computed overheat protection current value is abnormal is decided based on comparison of the newly computed overheat protection current value with the stored information relevant to the overheat protection current value.